fugacious vs transient

fugacious is not a noun while transient is a noun.

Word	Noun	Adjective	Verb	Adverb
fugacious	No	Yes	No	No
transient	Yes	Yes	No	No

As adjectives, fugacious and transient are synonyms defined as:

Other synonyms of fugacious include ephemeral, passing, short-lived, transitory.

fugacious (noun)	transient (noun)
	(physics) a short-lived oscillation in a system caused by a sudden change of voltage or current or load
	one who stays for only a short time

fugacious (adjective)	transient (adjective)
lasting a very short time	of a mental act; causing effects outside the mind
	lasting a very short time